Patients that are anesthetized during surgery are usually intubated. It has been desirable to measure the respiratory gases of such patients to determine the constituents of the respiratory gas. Specifically, analysis of the inspired and expired respiratory gas provides information regarding the amount of carbon dioxide (CO.sub.2), nitrous oxide (N.sub.2 O), and anesthetic agents the respiratory gas contains.
Anesthetic agents are present as a single agent gas or as a mixture of a number of agent gases during transition from one type of agent gas to another. Three of the most common anesthetic agent gases, other than nitrous oxide, are halothane, enflurane, and isoflurane. The agent gas that is administered to a patient must be carefully controlled by an anesthesiologist because of the great risk of supplying too much or too little. If too much is supplied the patient may die and if too little is supplied the patient may be subjected to needless pain.
In the past, the gas analyzers that were used to measure agent gases were the same devices that were used to measure end-tidal CO.sub.2 and N.sub.2 O. These devices include mass spectrometers and non-dispersive infrared gas analyzers ("infrared gas analyzer").
Mass spectrometers that are used for such gas measurements are usually part of operating room suites in which one spectrometer is shared among many rooms. Though a mass spectrometer measures a multiplicity of gases, it has the disadvantages of cost, maintenance and calibration requirements, slow response time, and non-continuous measurement. Infrared gas analyzers, though having the ability to measure the concentrations of inspired and end-tidal CO.sub.2 and N.sub.2 O, have not in the past simultaneously measured, or identified, multiple agent gases in real-time.
The present invention overcomes these and other problems of prior art devices that have been used to measure respiratory gases as will be shown in the remainder of the specification and in the attached drawings.